About three decades ago a small engine mechanic recommended it and I now use it in all my small engines. I thought that was interesting because if the stuff works he wouldn't be seeing as many engines coming through his shop.
What I observed was there is little, if any varnish buildup and with the right dose it stabilizes the fuel.
When my log splitter started running [bleep] my buddy who was also a small engine guy told me to purchase 91 octane or higher and toss in some seafoam. That was years ago and haven't had a problem since. The small engines seem to dislike the ethanol crap over time.
